1. Field of the Invention
This invention relates to a thermal management of a combustion engine and more particularly relates to supporting the efficient regeneration of an aftertreatment device such that an optimal fuel efficiency is achieved.
2. Description of the Related Art
Consumer demand for the benefits provided by the internal combustion engine, environmental concerns, and falling reserves of fossil fuel continue to spur improvements in the durability, fuel efficiency, and the emission's quality of the combustion engine. Competing performance demands, such as increasing fuel efficiency while reducing harmful emissions, provide ongoing engine development challenges. Many techniques of reducing emissions are well known in the art and substantially all of them adversely affect fuel efficiency. For example, a common catalytic converter must periodically achieve certain temperature thresholds, as a maintenance step, to oxidize particulates within the device (i.e. regenerate). In an alternate example, a diesel particulate filter collects soot that must be continually, or periodically, burned off by temperature increases in the exhaust stream passing through the device.
The preceding aftertreatment device examples illustrate the need of most aftertreatment devices for requisite heat that typically must be provided via the exhaust stream passing through the aftertreatment system. One common method to increase the temperature of the exhaust stream consists of adding extra fuel in-cylinder and/or down stream of an exhaust manifold during a portion of the combustion cycle (i.e. fuel dosing). Depending on the timing and the location where additional fuel is introduced efficiency may be reduced by a phase disturbance of the combustion cycle, unburned fuel lingering in the exhaust stream, and/or by decreasing the air to fuel ratio.
Another common approach to raise the temperature in the exhaust stream includes restricting the amount of air available for combustion, once again effectively reducing the air to fuel ratio. One example of how this may be accomplished includes creating a restriction in the exhaust stream, such as by choking the exhaust flow through a variable geometry turbocharger. Once again, however, this method generates a backpressure on the engine, which reduces the work efficiency of the engine. Temperature increases may need to be either periodic and/or fall within specific ranges to limit the amount of nitrous oxides that may be generated in the high heat environment. Many present applications of the internal combustion engine face thermal control challenges that may impede the optimization of fuel efficiency, degrade the power output, generate thermal stress on aftertreatment components, and reduce the overall effectiveness of the aftertreatment system.